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I've got one of those 1-meter addressable RGB LED strips from Sparkfun (link) connected to an Arduino. The Arduino is powered by the recommended 9V DC 650mA power supply through the barrel jack.

According to the Sparkfun website and product video I should be able to power these from the 5V pin (also 1 data pin, and a ground connected). But when I do, the board gets really hot (untouchable). Also, if I try to set all the LEDs to white - they just fade down after a few seconds.

I'm guessing the LEDs are trying to draw too much power from the board? If so, what is the correct way to power both the Arduino and the LED strip (preferably from a single power supply)?

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2 Answers 2

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The regulator on the Arduino is a linear regulator, which means that it reduces the voltage by throwing the rest of the power away. At 9V and 650mA, it's throwing away (9V - 5V) * 650mA = 2.6 watts. This is a decent amount of power, and more than the regulator can handle.

Using a switching regulator instead would cause it to make up for the drop in voltage by using less current from the source; a 90% efficient switching regulator would waste only about 5V * 650mA * 10% = 325mW, which is easier for larger packages to disperse.

Look on eBay or DX or the like for a 5V or adjustable DC-DC switching module. Connect the input to your 9V source and the output (set to 5V) to both the 5V input on the Arduino and the 5V input on the LED strip.

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  • \$\begingroup\$ +1 for suggesting a switcher. (Also grats on 10k. :) ) \$\endgroup\$
    – JYelton
    Apr 4, 2014 at 5:05
  • \$\begingroup\$ Thanks, is this sort of thing ok? adafruit.com/products/276 \$\endgroup\$
    – user834466
    Apr 4, 2014 at 5:13
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    \$\begingroup\$ @user834466 The datasheet page 4 shows 20mA for each emitting color. With 60 of these packages, you'll have a total requirement of 3.6 A. The power supply you linked can only supply up to 2 A. Try this one instead. \$\endgroup\$
    – JYelton
    Apr 4, 2014 at 5:16
  • \$\begingroup\$ @user834466: I generally don't trust wall warts to give the desired voltage with any degree of accuracy; I would check the exact output voltage very carefully (preferably with a decent resistive load) before feeding any directly into the Arduino. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Apr 4, 2014 at 5:18
  • \$\begingroup\$ @JYelton will that also power the arduino, or is that just for the strip? \$\endgroup\$
    – user834466
    Apr 4, 2014 at 5:22
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The individual LEDs draw up to 60mA.

It looks like the hook-up guide is connecting five LEDs to an Arduino, about a 300mA maximum draw.

You're connecting 60 LEDs, that's over 3.5A maximum draw. It's not surprising that your board is getting hot or, when trying to draw the maximum (white), completely failing.

Use the external power connector to connect to a supply that can provide more current.

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  • \$\begingroup\$ Thanks for the info. I was hoping not to have to provide a 2nd power supply, but i guess this is the only way? Also, sorry I meant the demo video: sparkfun.com/videos#all/lyXX5xsy1sA here they are connecting the full 1m (seek to 2min 50). \$\endgroup\$
    – user834466
    Apr 4, 2014 at 5:08
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    \$\begingroup\$ @user834466 At the 2 minute mark, the host says "You will be going past the power requirements of what the Arduino can handle, so you would be powering it externally, and just using the Arduino to feed it the data signal." \$\endgroup\$
    – JYelton
    Apr 4, 2014 at 5:13
  • \$\begingroup\$ Thanks @JYelton, I didn't hear that part. Could I power the strip via the VIN pin in that case? \$\endgroup\$
    – user834466
    Apr 4, 2014 at 5:18
  • \$\begingroup\$ @user834466: You don't want the power going through the board at all if you can help it. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Apr 4, 2014 at 5:19
  • \$\begingroup\$ @user834466 Do, however, connect the grounds together. \$\endgroup\$
    – Samuel
    Apr 4, 2014 at 5:20

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